An SPH-based modelling approach to enhance the predictability of nano-scale mechanical machining

Shen, Hao 2024. An SPH-based modelling approach to enhance the predictability of nano-scale mechanical machining. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Atomic Force Microscope (AFM) probe-based mechanical machining has attracted the attention of the research community over the past twenty years as a potential tool for conducting micro and nano-scale mechanical material removal operations. This technique has demonstrated potential applications in mechanical, physical, chemical, biomedical and other interdisciplinary fields. However, a current research issue affecting its wider utilisation is the lack of accurate simulation tools to quantitatively predict the process outcomes. In this context, this Thesis explores the possibility of employing a mesh-free numerical method, namely Smooth Particle Hydrodynamics (SPH), to simulate several scenarios in AFM-based micro and nano-scale machining. Up to Chapter 4, the SPH modelling of nano-indentation was conducted using the ANSYS/LS-DYNA software using three different published studies as benchmarks. The SPH outcomes were found to compare well against finite element modeling and experimental results reported in benchmark studies in the context of both micro and nano-scale indentation processes. These feasibility studies conducted in this chapter suggested that the SPH mthod is a technique with the potential to be considered more widely by researchers investigating high strain, or strain rate, deformation phenomena on the nanoscale. For example, the presented research on the development of an SPH-based nano-indentation model lays the foundations towards formulating a more comprehensive SPH model for the accurate simulation of nanoscale tool-based machining processes in following Chapters. Based on the above conclusion, Chapter 5 of the Thesis extended the complexity of the implemented SPH model by considering the influence of the lateral motion between the indenter and the sample following initial nano-indentation. In particular, the simulation of the nano-machining process on copper using SPH was conducted with a specific view to study the influence of the selected material constitutive model, namely the Johnson-Cook and the elasto-plastic models. The Abstract ii simulated cutting and normal forces as well as the machined topography using both constitutive models were compared with the experimental work from existing literature. The SPH simulation results showed that using the Johnson-Cook material model, cutting and normal forces were closer to the experimental data compared to the results obtained with the elasto-plastic model. The results also showed that the cross-sectional profile of simulated nano-grooves using the Johnson-Cook model was closer to the experimental results. Therefore, the work conducted in Chapter 5 showed that the selection of the Johnson-Cook model is preferable for the SPH modelling of the nano-machining process. The last part of the Thesis (i.e. Chapter 6) developed a novel SPH model in the context of AFM tip-based dynamic ploughing lithography (DPL), in which the AFM tip vibrates in vertical direction while machining in the horizontal direction. The SPH-predicted forces and surface topographies of AFM probe-based DPL were comprehensively investigated. The SPH simulation results showed that 3D periodic nanostructures with triangular-shaped profiles were clearly visible with a relatively large vibration period. In addition, the height of the generated periodic nanostructure was subject to the viewing direction. These SPH simulation results shed light on the possibility of employing AFM-based DPL for fabricating 3D periodic nanostructures with triangular-shaped or sinusoidal profile waveforms. In summary, the implemented SPH models in this Thesis could be used as a suitable first approximation to predict the process outcomes during both nano-indentation and nano-machining. In addition, the SPH simulation results reported in this Thesis theoretically confirmed the possibility of employing AFM-based DPL for fabricating triangular-shaped waveform nanostructures with desired dimensions.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Uncontrolled Keywords:	1). Smooth Particle Hydrodynamics (SPH) 2). AFM Probe-based Mechanical Machining 3).Nano-scale Scratching 4). Dynamic Ploughing Lithography 5). Johnson-Cook Material Model 6). Periodic Nanostructure
Date of First Compliant Deposit:	10 February 2025
Last Modified:	10 Feb 2025 10:08
URI:	https://orca.cardiff.ac.uk/id/eprint/176034

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